1. Field of the Invention
The present invention related to a process for preparing a 1,3-disubstituted urea, and more particularly to a process for preparing a 1,3-disubstituted urea which is useful as an intermediate for the preparation of pharmaceuticals and agricultural chemicals.
2. Discussion of Related Art
Conventionally, as methods for preparing a 1,3-disubstituted urea, there have been proposed, for instance, (1) a method for preparing a 1,3-disubstituted urea comprising reacting a primary amine with phosgene as disclosed in J. Org. Chem., 16 (1951) p.1879-1890, (2) a method for preparing a 1,3-disubstituted urea comprising reacting a primary amine with isocyanate as disclosed in J. Org. Chem., 16 (1951) p.1879-1890, (3) a method for preparing a 1,3-disubstituted urea comprising reacting a primary amine or a secondary amine with carbon monoxide as disclosed in Japanese Unexamined Patent Publication No. 60-163853, (4) a method for preparing a 1,3-disubstituted urea comprising reacting a primary amine with carbon dioxide as disclosed in Japanese Examined Patent Publication No. 62-9107, (5) a method for preparing a 1,3-disubstituted urea comprising reacting a primary amine with a cyclic carbonic acid ester as disclosed in Japanese Examined Patent Publication No. 62-17572, (6) a method for preparing a 1,3-disubstituted urea comprising reacting a primary amine or a secondary amine with bis(4-nitrophenyl)carbonate as disclosed in Synthesis, 6 (1989) p.423-425, and the like.
However, the above methods (1) and (2) have defects in workability and safety because those methods necessitate toxic phosgene and isocyanate as starting materials.
The above methods (3) to (5) have defects in the yield of a 1,3-disubstituted urea. In order to increase the yield, the above methods necessitate severe reaction conditions such as high temperatures and high pressures or an excess amount of a primary amine. When the severe reaction conditions are employed, a large and complex apparatus is necessitated. Also, when the excess amount of the primary amine is used, there is a defect in the separation and recovery of the unreacted primary amine after the reaction.
Also, the above method (6) has a defect in economics because the method necessitates expensive bis(4-nitrophenyl)carbonate as a starting material.
An object of the present invention is to provide a process for preparing a 1,3-disubstituted urea, excellent in workability, safety, yield and economics.
These and other objects of the present invention will be apparent from the following descriptions.